This invention relates to novel antibacterial agents. More particularly, the invention relates to novel antibacterial agents that act as multibinding agents. The multibinding agents of the invention comprise from 2-10 ligands covalently connected by a linker or linkers, wherein each of said ligands in their monovalent (i.e. unlinked) state have the ability to bind to a cell surface or a precursor used in the synthesis of the bacterial cell wall and thereby interfere with the synthesis of the precursor and the cell wall. The manner in which the ligands are linked is such that the multibinding agents so constructed demonstrate an increased biological and/or therapeutic effect as compared to the same number of unlinked ligands available for binding to the ligand binding site.
The invention also relates to pharmaceutical compositions comprising a pharmaceutically acceptable excipient and an effective amount of a compound of the invention, and to methods of using such compounds and pharmaceutical compositions containing them as antibacterial agents.
Still further, the invention also relates to methods of preparing such compounds.
A bacterial cell wall consists of linear polysaccharide chains that are cross-linked by short peptides. This arrangement confers mechanical support to the cell wall, and prevents the bacteria from bursting due to the high internal osmotic pressure. Cross linking takes place after lipid-linked disaccharide-pentapeptide constructs (lipid intermediate II) are incorporated into linear polysaccharide chains by a transglycolase enzyme. The cross-linking reaction is the last step of the synthesis of the cell wall, and is catalyzed by an enzyme known as peptidoglycan transpeptidase.
One method by which antibacterial agents exert their antibacterial activity is by inhibiting the transglycosylase enzyme, thus interfering with the penultimate step of the synthesis of the bacteria cell wall. Although not wishing to be bound by theory, it is believed that a glycopeptide, for example vancomycin, binds with high affinity and specificity to N-terminal sequences (L-lysyl-D-alanyl-D-alanine in vancomycin-sensitive organisms) of peptidoglycan precursors known as lipid intermediate II. By binding to and sequestering these precursors, vancomycin prevents their utilization by the cell wall biosynthesis machinery. In a formal sense, therefore, vancomycin inhibits the bacterial transglycosylase that is responsible for adding lipid intermediate II subunits to growing peptidoglycan chains. This step preceeds the cross-linking transpeptidation step which is inhibited by beta-lactams antibiotics. It is likely that vancomycin also inhibits transpeptidation which involves the D-alanyl-D-alanine termini; however, as this step occurs subsequent to transglycosylation, inhibition of transpeptidation is not be directly observed.
Antibacterial agents have proved to be important weapons in the fight against pathogenic bacteria. However, an increasing problem with respect to the effectiveness of antibacterial agents relates to the emergence of strains of entrococci that are highly resistant to such agents; for example, vancomycin-resistant entrococci (VRE), which are also multi-drug resistant. It would therefore be highly desirable to find antibacterial agents that are active against a broad spectrum of bacteria, in particular resistant strains such as VRE. It would be also be advantageous to discover antibacterial agents that demonstrate high activity and selectivity toward their targets, and are of low toxicity.
We have discovered that covalent connection of two or more ligands (antibacterial agents) by a linker or linkers provides a multibinding agent that affords an improved biological effect when compared to the same concentration of unlinked ligand (i.e. in its monomeric state), or when compared to a ligand monomer coupled to the linker only. That is to say, an improved biological and/or therapeutic effect of the multibinding agent is obtained as measured against that achieved by the same number of unlinked ligands available for binding to the ligand binding site of the peptidoglycan transglycosylase enzyme substrate.
A preferred ligand is vancomycin. Particularly preferred are vancomycin bivalent compounds, which demonstrate greatly enhanced biological effect when compared to vancomycin monomer, or vancomycin monomer to which is attached the linking structure. They are also highly effective when tested against VRE strains.
Although not wishing to be bound by any particular theory or proposed mechanism of action, it is believed that the surprising activity of the compounds of the invention arises from their ability to bind in a multivalent manner with their target and thus lower the energetic costs of binding (i.e. the phenomena of energetically coupled binding), which is produced by the optimum positioning of two or more molecules of a ligand in relationship to its binding site, i.e., a multivalent interaction. That is to say, the compounds act as multibinding agents, in which ligands that are covalently attached by a linker or linkers simultaneously (or contemporaneously) bind to multiple binding sites on another component, such as an enzyme substrate.
Vancomycin derivatives are disclosed in Patent Applications EP 0 802 199, EP 0 801 075, EP 0 667 353, WO 97/28812, WO 97/38702, and in JACS 118, pp 13107-13108 (1996), JACS 119, pp 12041-12047 (1997), and JACS 116, pp 4573-4590 (1994). The disclosures of these and other documents referred to throughout this application (e.g., in the Pharmacology section of the Detailed Description of the Invention) are incorporated herein by reference.
This invention addresses the above needs by providing novel multibinding agents. Accordingly, in one aspect, the present invention relates to novel multibinding agents;
wherein a multibinding agent comprises 2-10 ligands, which may be the same or different, covalently connected by a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a transglycosylase enzyme substrate.
The preferred multibinding agents are represented by Formula I:
(L)p(X)qxe2x80x83xe2x80x83Formula I
in which L is a ligand that may be the same or different at each occurrence;
X is a linker that may be the same or different at each occurrence;
p is an integer of 2-10; and
q is an integer of 1-20;
or a salt thereof,
wherein each of said ligands comprises a ligand domain capable of binding to a transglycosylase enzyme substrate, thereby modulating the activity of the enzyme substrate. Preferably q is less than p. More preferably p is 2 and q is 1. Particularly preferred is the compound of Formula I wherein L at each occurrence represents optionally substituted vancomycin; and X represents a linker between any hydroxyl group, carboxyl group or amino group of the first vancomycin to any hydroxyl group, carboxyl group or amino group of the second vancomycin. In a preferred embodiment, the linker, X, is:
xe2x80x94NHxe2x80x94R6xe2x80x94NHxe2x80x94C(O)xe2x80x94R7xe2x80x94C(O)xe2x80x94NHxe2x80x94R8xe2x80x94NHxe2x80x94
wherein R6, R7, and R8 are optionally substituted alkylene, when X connects the [C] terminus of a first glycopeptide to the [C] terminus of a second glycopeptide.
In another preferred embodiment, the linker, X, is:
xe2x80x94R6xe2x80x94NHxe2x80x94C(O)xe2x80x94R7xe2x80x94C(O)xe2x80x94NHxe2x80x94R8xe2x80x94
wherein R6, R7, and R8 are optionally substituted alkylene, when X connects the [V] terminus of a first glycopeptide to the [V] terminus of a second glycopeptide.
In still another preferred embodiemt, the linker, X is:
xe2x80x94NHxe2x80x94R6xe2x80x94NHxe2x80x94C(O)xe2x80x94R7xe2x80x94C(O)xe2x80x94NHxe2x80x94R8xe2x80x94
xe2x80x94NHxe2x80x94R6xe2x80x94NHxe2x80x94C(O)xe2x80x94R7xe2x80x94 or
xe2x80x94NHxe2x80x94R6xe2x80x94
wherein R6, R7, and R8 are optionally substituted alkylene, when X connects the [C] terminus of a first glycopeptide to the [V] terminus of a second glycopeptide.
In a second aspect, the invention relates to a method of treatment of mammals having a disease state that is treatable by an antibacterial agent, comprising administering a therapeutically effective amount of a novel multibinding agent thereto;
wherein a multibinding agent comprises 2-10 ligands, which may be the same or different, covalently connected by a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a transglycosylase enzyme substrate. The preferred multibinding agent is a compound of Formula I, or a mixture of compounds of Formula I.
In a third aspect, the invention relates to a method of treatment of mammals having a bacterial disease characterized by resistance to vancomycin, comprising administering a therapeutically effective amount of a multibinding agent as defined above, preferably a compound of Formula I, thereto, or a mixture of multibinding agents.
In a fourth aspect, the invention relates to a pharmaceutical composition comprising a therapeutically effective amount of one or more multibinding agents, or a pharmaceutically acceptable salt thereof, said multibinding agent comprising 2-10 ligands, which may be the same or different, covalently connected by a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a transglycosylase enzyme substrate, admixed with at least one pharmaceutically acceptable excipient, wherein the multibinding agent is preferably a compound of Formula I.
In a fifth aspect, the invention relates to processes for preparing the multibinding agents of the invention.